The present invention relates to easy-open container ends, in particular to the design of rupturable score lines which define a panel displacable by action of an opening tab. The present invention further relates to an improved die design for making score lines of improved design in such container ends.
Easy-open containers are well known in the beverage industry, and typically comprise a two-piece construction consisting of a container body and a container end. The container body and container end are typically made of thin gauge aluminum and joined to withstand internal pressures commonly associated with carbonated beverages.
Various easy-open features have been incorporated in container end walls. In a typical configuration, an opening tab attached to a container end wall may be rotated to exert axial pressure and displace a panel or tongue defined by rupturable score lines. The rupturable score lines are stamped into container end walls by score die sets of mating score dies and anvils. The rupturable score lines typically involve tight manufacturing tolerances because material thicknesses generally range in thousandths and ten-thousandths of inches. Thus, while rupture of the score line is desired, sufficient score line residual must remain to resist the internal container pressures. A typical score line design and container end known in the prior art are shown in FIGS. 1 and 2.
As production continues, score lines become weaker with die wear, and score line residual increases. Opening failures result with greater frequency as tearing and separation of the panel from the container end wall along weaker score lines stops prematurely. Score line residual may also be undesirably effected by factors other than die wear. Typically, score dies and mating anvils used to stamp score lines are mounted by three bolts to equipment at a stamping station. Uneven draw upon or overtorquing of the mounting bolts may cause distortion in the die or anvil surfaces.
In addition to the score line residual, rupture along the score line is typically facilitated by providing reinforcement of the container end wall and panel. To provide support and stiffness thereto, means for reinforcing, such as raised beads (also known as ribs or beams), and raised areas on the container end wall and panel are pressed into the material of the container end. The need for, and design of the various known means for reinforcing will vary depending upon the material thickness used.
It remains, however, that opening failures in easy-open container ends continue to occur with unacceptable frequency with known designs. Accordingly, further improvements are needed to decrease container opening failures and improve the operation of dies used to stamp score lines in container ends for easy-open containers.